[squid-users] TCP_MISS/504 in cache_peer

[Amos Jeffries]

On 30/06/2015 8:21 p.m., Stakres wrote:
> Anthony, Amos,
> 
> The 2 squid are kid/parent each of them (both sibling).

I'm being pedantic about this because the operations possible with a
parent proxy are very different from those done with a sibling proxy.

> So, when one aks the second, they play the role of kid -> parent, am I right
> ?

No. They play the roles of client->server. A kid->parent pair also plays
those client->server roles, but the conditions are different.

In particular parent can be an origin, sibling can only be a proxy or
cache. The cache controls are different, and in your case digesting is
telling the main proxy that its sibling has a cached object available.


> 
> Here is the way:
> Squid1 checks the Squid2 and gets that:
> ... user-ip TCP_MISS/504 708 GET
> http://code.jquery.com/ui/1.10.3/jquery-ui.js - CD_SIBLING_HIT/10.1.1.2 ...
> Squid2 replies that to the Squid1:
> ... squid1-ip TCP_MISS/504 478 GET
> http://code.jquery.com/ui/1.10.3/jquery-ui.js - HIER_NONE/- text/html
> 
> I did many wget with "unavailable" objects from both squid servers, i can
> get the objects correctly.
> I'll disable the sibling to check if we still have TCP_MISS/504, keep you
> posted...
> 
> As the 2 squid are in production at the ISP datacenter, not sure I could
> apply a debug...
> They do have the same route connected to 2 mikrotik (squid1 -> mikrotik1,
> squid 2 -> mikrotik2), both mikrotik connected to the same cisco router.
> Mangles/DNS/Gateway on mikrotiks are the same.

Then it is pointless to connect these proxies in the way you have done.

In particular the cache_peer "proxy-only" setting prevents them sharing
cached objects, so the sibling should only be used if links through the
Mikrotik go down. (any other use is a bug, and probably what you are
hitting).

So the sibling is being treated as a backup route if the upstream routes
are not working. But the sibling is physically wired to use the same
non-working upstream routes...


I'm wondering if the 504 is result of the sibling restrictions:
  Cache-Control:only-if-cached,max-age=0

Amos